Cracking of epitaxial MnAs films on GaAs(001)

We report the characteristics of the fracture of epitaxially grown MnAs films on GaAs(001) due to the large thickness or induced by annealing. Stresses arising from the thermal expansion mismatch and the structural phase transition can no longer be accommodated when the film thickness is beyond about 0.5 mu m, giving rise to cracking of the films. The cracks are inclined with respect to the c axis of MnAs, suggesting their initiation by a weak plane. For films thicker than about 2 mu m, the fracture extends to the substrates, where the in-plane crack angle changes from about 57 degrees to around 45 degrees as the cracking is dictated by the cleavage plane of the substrates. Even for films much thinner than 0.5 mu m, annealing results in a delamination from substrate as a consequence of the large thermal expansion and, plausibly, the oxidation of MnAs. We show that Mn capping suppresses the delamination as well as the oxidation during the annealing.